Catch exception thrown by PDC when updating a module
    
    We have observed in production that the messages:
    https://apps.fedoraproject.org/datagrepper/id?id=2020-dfeecf92-ebd8-4057-9758-f6ca86857b3b&is_raw=true&size=extra-large
    and
    https://apps.fedoraproject.org/datagrepper/id?id=2020-7b68144c-d96f-4dff-b52c-ca104f30ffef&is_raw=true&size=extra-large
    do not pass  the pdc_modules toddler.
    They lead to the following backtrace:
    ````
      File "/code/toddlers/runner.py", line 96, in __call__
        toddler.process(self.toddler_config[toddler.name], message)
      File "/code/toddlers/plugins/pdc_modules.py", line 93, in process
        pdc[pdc_api][uid]._ += {"koji_tag": message.body["koji_tag"]}
      File "/usr/lib/python3.8/site-packages/pdc_client/__init__.py", line 365, in __iadd__
        return self.client.__iadd__(value)
      File "/usr/lib/python3.8/site-packages/beanbag/namespace.py", line 142, in fn
        r = basefn(getattr(self, ".base"), getattr(self, ".path"),
      File "/usr/lib/python3.8/site-packages/beanbag/url_v1.py", line 137, in iadd
        self.make_request(path, "PATCH", {}, val)
      File "/usr/lib/python3.8/site-packages/beanbag/url_v1.py", line 154, in make_request
        raise BeanBagException(r,
    beanbag.bbexcept.BeanBagException: Bad response code: 404
    ````
    
    So apparently, we fail to update PDC for some reason (no idea what
    triggers the 404).
    
    This commit allows to log that exception and discard the action since:
    a) we don't know what triggered the 404
    b) the old pdc-updater client would ignore these errors just like we will
    do now and no-one seems to have complained about it
    
    So here we go!
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>